1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to apparatus for interfacing with integrated circuits and to methods of making the same.
2. Description of the Related Art
Many current integrated circuits consist of a chip or die enclosed within a package that is equipped with a plurality of connector pins for insertion into the socket of a circuit board. The die consists of a substrate composed of a semiconductor material such as silicon or germanium. One side of the substrate is provided with a plurality of circuit structures that makeup the integrated circuit and the other is left as relatively bare substrate material that is normally planarized via a polishing step.
Although packaging schemes for conventional integrated circuits are legion, many packages for individual die consist of mating halves of a ceramic or plastic material that are bonded together to form an enclosure. In some packaging schemes, the flat, non-circuit side of the die is secured to one half of the package and an electrical interconnections to the connector pins are made via a plurality of bonding wires soldered to bonding pads on the die and to portions of the connector pins. In other packaging schemes, the die is oriented in a so-called flip-chip fashion so that the die is oriented face down, that is, with the circuit structures of the integrated circuit facing downward and in contact with a plurality of minute solder bumps. The bumps are connected to the connector pins via bonding wires, metal traces, or the like. In still other packaging arrangements, multiple die are arranged in a multi-chip package and may be positioned in a flip-chip orientation or in other physical orientations.
As with most electrical devices, heat generation associated with processes such as I2R losses and capacitor charging and discharging presents challenges for the designer of die-based integrated circuits. Elevated chip operating temperatures impose constraints in several ways. To begin with, high operating temperatures restrict the types of materials that may be used to fabricate both the chip and the chip packaging. In addition, chip operating temperature has a direct impact on the maximum available switching speed and thus the overall speed performance of the integrated circuit. Furthermore, higher operating temperatures restrict the permissible operating voltage and ambient temperature environment of the chip. Lastly, chip life span is adversely impacted by higher operating temperatures. If the available mechanisms for integrated circuit heat dissipation cannot adequately handle the I2R heat propagation, compromises in the speed performance, the operating voltage, the applications and the design life span of the integrated circuit may have to be made.
In many conventional VLSI and ULSI circuit designs, engineers have turned to the use of heat sinks and forced convection in order to provide adequate cooling. A conductive heat transfer pathway is provided between the die and a heat sink that is coupled to the package. Many such conventional heat sinks consist of a plurality of metallic heat fins. The heat flow from the die to the die package is limited by the area of the die that is in contact with the package. In flip-chip packaging schemes, this contact surface area will normally be the area of the upward facing planar surface, that is, simply the area of the rectangular die. Since the contact area of the die is fixed, other means must be attempted to increase the heat flow therefrom, such as decreasing the temperature of the heat sink coupled to the package, either by increasing its size, by increasing the air flow across it to improve forced convective heat transfer, or by introducing a refrigerated fluid system to the package. Each of these solutions involves additional complexity and cost and may present space constraints on the placement of the integrated circuit in various products such as personal computers and other types of hardware.
The problems of heat dissipation are not limited to integrated circuit packaging. Indeed, various other structures used establish the requisite interfaces between integrated circuits and other devices form parts of the conductive heat transfer pathways to and from the integrated circuits. Two examples of these include circuit boards and sockets. Circuit boards provide a macro-level interface with devices, such as a computer. Various types of sockets are positioned on a typical circuit board to serve as plug-in sites for chips, other boards or devices. In both cases, the basic building material of the board or socket is generally electrically insulating and thus thermally resistive.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.